Propylene-based resin composition and film made of the same

ABSTRACT

Disclosed is a resin composition that comprises a propylene-based copolymer (X) consisting of two kinds of copolymeric components made up of propylene, α-olefin and optionally ethylene which are characterized by ethylene content and α-olefin content, the copolymer (X) exhibiting a specific endothermic behavior in DSC measurement and a copolymer (Y) made up of propylene and α-olefin and/or ethylene. The resin composition can afford a film superior in low-temperature heat sealability and antiblocking property.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a propylene-based resincomposition and to a film using the same.

[0003] The film of the present invention has optical characteristics,e.g. transparency and gloss, equal to those of conventionalpolypropylene films and is superior in low-temperature heat sealabilityand antiblocking property.

[0004] 2. Description of the Related Art

[0005] Polypropylene has been used widely in fields of films and sheetsdue to its excellent transparency, heat resistance and food sanitation.In recent years, a fabrication speed of bags has been increased and amaterial with good low-temperature heat sealability is awaited in thefield of packaging of foods and the like.

[0006] As a technique for achieving a good low-temperature heatsealability, Japan Patent No. 2882237 discloses that a polypropylenerandom copolymer which results from copolymerization of propylene and anα-olefin or of propylene, ethylene and an α-olefin performed insubstantial absence of solvent by use of a Ziegler-Natta catalyst andwhich has specific ranges of propylene content, ethylene content,a-olefin content and 20° C. xylene-soluble fraction content and also hasan increased comonomer content, and a film made of the copolymer aresuperior in low-temperature heat sealability. However, when the sealtemperature is lowered by increasing the comonomer content, problemswill arise; for example, if the comonomer content is increased to exceeda certain amount, rigidity will lower or the amount of fractions elutingin a solvent will increase, resulting in deterioration of foodsanitation.

[0007] In JP, 60-166455,A and Japan Patent No. 3070419, disclosed is apolypropylene laminate film having a surface layer made of apolypropylene copolymer of a very high α-olefin content. However,laminate films obtained by such techniques have a drawback of beingdeteriorated in view of its heat sealability by corona treatment and areproblematic in that a sufficient lowering of heat seal temperature cannot be achieved because too much increase of comonomer content willcause stickiness during a film forming step. Therefore, furtherimprovement has bee awaited.

SUMMARY OF THE INVENTION

[0008] The object of the present invention is to provide a polypropylenefilm having optical characteristics, e.g. transparency and gloss, equalto those of conventional polypropylene films and being superior inlow-temperature heat sealability and antiblocking property.

[0009] In a first aspect of the present invention, provided is apropylene-based resin composition comprising:

[0010] from 40 to 99% by weight of a propylene-based copolymer (X)consisting of from 1 to 30% by weight of component (A) that is acopolymeric component which is made up of propylene and an α-olefinhaving 4 or more carbon atoms and which satisfies Requirement 1 definedbelow or a copolymeric component which is made up of propylene, anα-olefin having 4 or more carbon atoms and ethylene and which satisfiesRequirement 1 and Requirement 2 defined below and from 70 to 99% byweight of component (B) that is a copolymeric component which is made upof propylene and an α-olefin having 4 or more carbon atoms and whichsatisfies Requirement 3 defined below or a copolymeric component whichis made up of propylene, an α-olefin having 4 or more carbon atoms andethylene and which satisfies Requirement 3 and Requirement 4 definedbelow, wherein the copolymer (X) satisfies Requirement 5 defined below,and

[0011] from 1 to 60% by weight of a propylene-based copolymer (Y) madeup of propylene and an α-olefin and/or ethylene, the copolymer (Y)having a content of propylene of from 86 to 97% by weight and a combinedcontent of ethylene and the (α-olefin of from 3 to 14% by weight,provided that each of the percentages of the amounts of the component(A) and the component (B) is based on the amount of the copolymer (X)and the sum of the percentages of the amounts of the components (A) and(B) is 100% by weight, each of the percentages of the amounts of thecopolymer (X) and the copolymer (Y) is based on the combined amount ofthe copolymers (X) and (Y), and the content of propylene in thecopolymer (Y) and the combined content of ethylene and the α-olefin inthe copolymer (Y) are respectively based on the combined amount ofpropylene, ethylene and the α-olefin in the copolymer (Y):

[0012] Requirement 1: The content of α-olefin having 4 or more carbonatoms in the component is not less than 1 mol % but less than 15 mol %.

[0013] Requirement 2: The content of ethylene in the component is notmore than 5 mol %.

[0014] Requirement 3: The content of the α-olefin having 4 or morecarbon atoms in the component is from 15 mol % to 30 mol %.

[0015] Requirement 4: The content of ethylene in the component is notmore than 5 mol %.

[0016] Requirement 5: In measurement of a DSC curve of the material, theamount of heat absorption within the temperature range of from T−10 (°C.) to T+10 (° C.) accounts for from 15 to 36% the amount of heatabsorption within the temperature range of from 53° C. to 170° C.,wherein T denotes a temperature (° C.) at which a maximum endothermicpeak appears.

[0017] In a second aspect, the present invention provides apropylene-based resin composition of the first aspect, wherein thecopolymer (X) is a copolymer such that the component (A) is polymerizedin a first step and the component (B) is polymerized in a second step orin the second and later steps performed in the presence of the component(A) which has been formed in the first step.

[0018] In a third aspect, the present invention provides apropylene-based resin composition of the second aspect, wherein thecopolymer (X) is a copolymer obtained by performing the polymerizationfor forming the component (A) in the absence of an inert solvent andperforming the polymerization for forming the component (B) in a gasphase.

[0019] In a fourth aspect, the present invention provides apropylene-based resin composition provided in the first aspect, whereinthe copolymer (X) is a copolymer obtained by polymerizing propylene andan α-olefin having 4 or more carbon atoms or polymerizing propylene, anα-olefin having 4 or more carbon atoms and ethylene in the presence of asolid catalyst component containing Ti, Mg and halogen as essentialcomponents.

[0020] In the fifth aspect, the present invention provides a film havinga layer made of the propylene-based resin composition provided in thefirst aspect.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0021] The propylene-based resin composition of the present inventioncomprises:

[0022] a propylene-based copolymer (X) consisting of component (A) thatis a copolymeric component which is made up of propylene and an α-olefinhaving 4 or more carbon atoms and which satisfies Requirement 1mentioned later or a copolymeric component which is made up ofpropylene, an α-olefin having 4 or more carbon atoms and ethylene andwhich satisfies Requirement 1 and Requirement 2 mentioned later andcomponent (B) that is a copolymeric component which is made up ofpropylene and an α-olefin having 4 or more carbon atoms and whichsatisfies Requirement 3 mentioned later or a copolymeric component whichis made up of propylene, an α-olefin having 4 or more carbon atoms andethylene and which satisfies Requirement 3 and Requirement 4 mentionedlater, wherein the copolymer (X) satisfies Requirement 5 mentionedlater, and

[0023] a propylene-based copolymer (Y) made up of propylene and anα-olefin and/or ethylene.

[0024] (i) Copolymer (X)

[0025] (i-A) Component (A)

[0026] Component (A) is a copolymeric component made up of propylene andan α-olefin having 4 or more carbon atoms or a copolymeric componentmade up of propylene, an α-olefin having 4 or more carbon atoms andethylene, and preferably is a copolymeric component made up of propyleneand an α-olefin having 4 or more carbon atoms.

[0027] The content of the α-olefin having 4 or more carbon atoms incomponent (A) is not less than 1 mol % but less than 15 mol %(Requirement 1), preferably 1 mol % or more and less than 12 mol %, andmore preferably from 1 mol % to 10 mol %. When a copolymeric componenthaving a content of α-olefin having 4 or more carbon atoms of less than1 mol % is contained in place of component (A), the low-temperature heatsealability will become poor.

[0028] The content of ethylene in component (A) is up to 5 mol %(Requirement 2), and preferably up to 3 mol %. When the amount ofethylene contained in component (A) exceeds 5 mol %, a film made of theresin composition may get whitened or may come to have less rigiditywith time.

[0029] (i-B) Component (B)

[0030] Component (B) is a copolymeric component made up of propylene andan α-olefin having 4 or more carbon atoms or a copolymeric componentmade up of propylene, an α-olefin having 4 or more carbon atoms andethylene, and preferably is a copolymeric component made up of propyleneand an α-olefin having 4 or more carbon atoms.

[0031] The content of the α-olefin having 4 or more carbon atoms incomponent (B) is from 15 mol % to 30 mol % (Requirement 3), andpreferably from 15 mol % to 25 mol %. When a copolymeric componenthaving a content of α-olefin having 4 or more carbon atoms of more than30 mol % is contained in place of component (B), a film made of theresin composition may have a low rigidity.

[0032] The content of ethylene in component (B) is up to 5 mol %(Requirement 4), and preferably up to 3 mol %. When the amount ofethylene contained in component (B) exceeds 5 mol %, a film made of theresin composition may get whitened or may come to have less rigiditywith time.

[0033] Examples of the α-olefin having 4 or more carbon atoms used incomponents (A) and (B) include 1-butene, 2-methyl-1-propene, 1-pentene,2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 2-ethyl-1-butene,2,3-dimethyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene,4-methyl-1-pentene;, 3,3-dimethyl-1-butene, 1-heptene, methyl-1-hexene,dimethyl-1-pentene, ethyl-1-pentene, trimethyl-1-butene,methylethyl-1-butene, 1-octene, methyl-1-pentene, ethyl-1-hexene,dimethyl-1-hexene, propyl-1-heptene, methylethyl-1-heptene,trimethyl-1-pentene, propyl-1-pentene, diethyl-1-butene, 1-nonene,1-decene, 1-undecene and 1-docedene. Preferred are 1-butene, 1-pentene,1-hexene and 1-octene. More preferred are 1-butene and 1-hexene in viewof copolymerization property, economical efficiency, etc.

[0034] Examples of components (A) and (B) include propylene-1-butenecopolymers, propylene-1-hexene copolymers, propylene-ethylene-1-butenecopolymers and propylene-ethylene-1-hexene copolymers. Preferred arepropylene-1-butene copolymers and propylene-1-hexene copolymers. Thekinds of monomers constituting component (A) may be different from orthe same as those of component (B). Component (A) and component (B) maybe chemically bonded together or not bonded. Alternatively, a mixturecomprising those chemically bonded and those not chemically bonded mayalso be available.

[0035] The copolymer (X) must satisfy the following requirement(Requirement 5).

[0036] Requirement 5: In measurement of a DSC curve of the material, theamount of heat absorption within the temperature range of from T−10 (°C.) to T+10 (° C.) accounts for from 15 to 36% the amount of heatabsorption within the temperature range of from 53 to 170° C., wherein Tdenotes a temperature (° C.) at which a maximum endothermic peakappears.

[0037] A sample used in the measurement of a DSC curve is specifically a0.5 mm thick sheet obtained by hot-press molding of a material for test(specifically, preheating the material at 230° C. for 5 minutes,followed by increasing pressure to 50 kgf/cm²G over 3 minutes, followedby maintaining the pressure for 2 minutes, followed by cooling at 30° C.at 30 kgf/cm²G for minutes).

[0038] In the present invention, the measurement of a DSC curve iscarried out under the following conditions. A DSC curve is obtained insuch a manner that using a differential scanning calorimeter(manufactured by Perkin-Elmer, Inc., Model DSC-7), about 10 mg of aspecimen sampled from the above-mentioned sheet is heated at 220° C. for5 minutes under a nitrogen atmosphere, followed by cooling to 150° C. ata temperature decrease speed of 300° C./minute, followed by holding at150° C. for one minute, followed by cooling to 50° C. at a temperaturedecrease speed of 5° C./minute, followed by holding at 50° C. for oneminute, and followed by heating from 50° C. to 180° C. at a temperatureincrease speed of 5° C./minute.

[0039] Calculated is the area of a region surrounded by the DSC curveand a straight line (baseline) obtained by joining a point at 53° C. anda point at 170° C., which area is called a first area. On the otherhand, calculated is the area of a region surrounded by the baseline andthe DSC curve within the temperature range of from T−10 (° C.) to T+10(° C.), wherein T denotes a temperature (° C.) at which a maximumendothermic peak appears, which area is called a second area. The ratioof the second area to the first area is defined as a ratio of the amountof main heat absorption to the amount of total heat absorption in themeasurement of the DSC curve.

[0040] In the copolymer (X), the thus obtained ratio of the amount ofmain heat absorption to the amount of total heat absorption is from 15to 36% (Requirement 5), preferably from 18 to 35%, more preferably from20 to 34%, and still more preferably from 22 to 32%. If the ratio is toogreat, the distribution of the melting point of the copolymer (X)becomes narrow to cause stickiness of a film made of the composition ina temperature range for film formation, which may result indeterioration of operation efficiency or deterioration of coronatreatment resistance of the film. On the other hand, if the ratio is toosmall, the crystallization rate at the time of film formation becomessmall, which may deteriorate the operation efficiency of film formation.

[0041] The contents of components (A) and (B) in the copolymer (X) arefrom 1 to 30% by weight of component (A) and from 70 to 99% by weight ofcomponent (B), preferably from 5 to 30% by weight of component (A) andfrom 70 to 95% by weight of component (B), and more preferably from 5 to20% by weight of component (A) and from 80 to 95% by weight of component(B), provided that each of the percentages of the amounts of component(A) and component (B) is based on the amount of the copolymer (X) andthe sum of the amounts of components (A) and (B) is 100% by weight.

[0042] When the content of component (A) is less than 1% by weight (thatis, the content of component (B) exceeds 99% by weight), serioussticking may occur during formation of a film from the composition. Whenthe content of component (A) exceeds 30% by weight (that is, the contentof component (B) less than 70% by weight), a film made of thecomposition may have an insufficient low-temperature heat sealability.

[0043] The copolymer (X) can be obtained, for example, by polymerizingcomponent (A), which is a copolymer of propylene, an α-olefin having 4or more carbon atoms and optionally ethylene, in a first step andsubsequently polymerizing component (B), which also is a copolymer ofpropylene, an α-olefin having 4 or more carbon atoms and optionallyethylene, in a second step or in the second and later steps carried outin the presence of component (A) which has been formed in the firststep.

[0044] The production of the copolymer (X) can be carried out using aknown polymerization catalyst. Examples of the catalyst includeZiegler-Natta type catalysts and metallocene type catalysts. Preferredare catalysts containing Ti, Mg and halogen as essential components.

[0045] For example, Ti-Mg-based catalysts comprising a solid catalystcomponent obtained by compounding a magnesium compound with a titaniumcompound, and catalyst systems comprising such a solid catalystcomponent, an organoaluminum compound and a third component, e.g. anelectron-donating compound, are mentioned. Specific examples arecatalyst systems disclosed, for example, in JP, 61-218606,A, JP,61-287904,A and JP, 7-216017,A.

[0046] The organoaluminum compound is not particularly restricted.Preferred are triethylaluminum, triisobutylaluminu, a mixture oftriethylaluminum and diethylaluminum chloride, andtetraethyldialumoxane.

[0047] The electron-donating compound is not particularly restricted.Preferred are cyclohexylethyldimethoxysilane,tert-butyl-n-propyldimethoxysilane, tert-butylethyldimethoxysilane, anddicyclopentyldimethoxysilane.

[0048] As a polymerization method, available are, for example, solventpolymerization which uses an inert solvent typified by hydrocarboncompounds such as hexane, heptane, octane, decane, cyclohexane,methylcyclohexane, benzene, toluene and xylene, bulk polymerizationwhich use a liquid monomer as a solvent, and gas phase polymerizationwhich is carried out in a gaseous monomer. Preferred are bulkpolymerization and gas phase polymerization where it is easy to performpost treatment. These polymerizations may be in a batch mode or in acontinuous mode.

[0049] In the above polymerization methods, the polymerization used inthe first step and the polymerization used in the second step or in thesecond and later steps may be the same or different. In view ofpolymerization activity and ease of post treatment, it is preferred thatthe first step be a step in which polymerization is carried out in theabsence of an inert solvent and the second step or the second and latersteps be a step or steps in which polymerization is carried out in a gasphase. The polymerization in the first step and the polymerization inthe second step or in the second and later steps may be carried out inthe same polymerization vessel (reactor) or different polymerizationvessels (reactors).

[0050] The production method may be, for example, solvent-solventpolymerization, bulk-bulk polymerization, gas phase-gas phasepolymerization, solvent-gas phase polymerization, bulk-gas phase-gasphase polymerization, solvent-gas phase-gas phase polymerization, andbulk-gas phase-gas phase polymerization. Preferred are bulk-gas phasepolymerization, gas phase-gas phase polymerization and bulk-gasphase-gas phase polymerization.

[0051] The polymerization temperature used in the first step is notparticularly limited, but usually is from 20 to 150° C., and in view ofproductivity and controllability of the contents of components (A) and(B), preferably from 35 to 95° C.

[0052] The polymerization temperature used in the second step or in thesecond and later steps may be equal to or different from that used inthe first step. It is usually from 20 to 150° C., and preferably from 35to 95° C.

[0053] In the above-mentioned production methods, post treatments, e.g.inactivation of a catalyst, removal of a solvent, removal of monomers,drying and granulation may optionally be carried out.

[0054] Examples of the copolymer (X) include(propylene-1-butene)-(propylene-1-butene) copolymers,(propylene-1-butene)-(propylene-ethylene-1-butene) copolymers,(propylene-ethylene-1-butene)-((propylene-1-butene) copolymers,(propylene-ethylene-1-butene)-(propylene-ethylene-1-butene) copolymers,and (propylene-1-hexene)-(propylene-1-hexene) copolymers. Preferred are(propylene-1-butene)-(propylene-1-butene) copolymers and(propylene-1-hexene)-(propylene-1-hexene) copolymers. More preferableare (propylene-1-butene)-(propylene-1-butene) copolymers. With regard totwo pairs of parentheses in each copolymer listed above, the former pairand the latter pair indicate component (A) and component (B),respectively.

[0055] The melt flow rate (MFR) of the copolymer (X) measured at 230° C.is not particularly restricted, but, in view of flowability or filmformability, is preferably from 0.1 to 50 g/10 min, more preferably from1 to 20 g/10 min. To control flowability, the MFR may be changed by anappropriate method, e.g. addition of organic peroxide, during meltkneading.

[0056] (ii) Copolymer (Y)

[0057] The copolymer (Y) used in the present invention is a copolymermade up of propylene and an α-olefin having 4 or more carbon atomsand/or ethylene. The content of propylene in the copolymer (Y) is from86 to 97% by weight, preferably from 88 to 97% by weight, and morepreferably from 88 to 96.5%by weight. When the copolymer (Y) is acopolymer made up of propylene and an α-olefin having 4 or more carbonatoms, the proportion of the α-olefin is a value obtained by subtractingthe above-mentioned propylene content from 100% by weight. When thecopolymer (Y) is a copolymer made up of propylene and ethylene, theproportion of ethylene is a value obtained by subtracting theabove-mentioned propylene content from 100% by weight. When thecopolymer (Y) is a copolymer made up of propylene, an α-olefin having 4or more carbon atoms and ethylene, the combined proportion of theα-olefin and ethylene is a value obtained by subtracting theabove-mentioned propylene content from 100% by weight. The weight ratioof the α-olefin to the ethylene is preferably from 30/70 to 90/10.

[0058] The copolymer (Y) is preferably a random copolymer made up ofpropylene and an α-olefin having 4 or more carbon atoms and/or ethylene,and specifically, a crystalline ethylene-propylene random copolymer, anethylene-butene-1-propylene random terpolymer or the like conomomercontents of which are within the above-mentioned ranges. In view of heatseal temperature of a film obtained from the resin composition of thepresent invention, the melting point of the copolymer (Y) is preferablylower than 155° C., and more preferably not higher than 150° C.

[0059] In view of the antiblocking property of a film obtained from theresin composition of the present invention, the content of a 20° C.xylene-soluble fraction of the copolymer (Y) is preferably up to 15% byweight, more preferably up to 13% by weight, and still more preferablyup to 10% by weight.

[0060] The MFR of the copolymer (Y) is preferably from 0.1 to 50 g/10min, more preferably from 1 to 20 g/10 min, and still more preferablyfrom 1 to 15 g/10 min.

[0061] In the propylene-based resin composition of the presentinvention, the weight ratio of the copolymer (X) to the copolymer (Y) isfrom 40/60 to 99/1, preferably from 50/50 to 95/5, and more preferablyfrom 50/50 to 90/10. If the proportion of the copolymer (X) is less than40% by weight, a film obtained from the resin composition will have aninsufficient low-temperature heat sealability, whereas when exceeding99% by weight, a film obtained from the resin composition will have apoor antiblocking property.

[0062] The propylene-based resin composition of the present inventionpreferably contains a fraction elutable in xylene (20° C.) in an amountof up to 30% by weight, more preferably up to 25% by weight.

[0063] The MFR of the propylene-based resin composition of the presentinvention is preferably from 0.1 to 50 g/10 min, more preferably from 1to 20 g/10 min, and still more preferably from 2 to 15 g/10 min.

[0064] The propylene resin composition of the present invention can beobtained by dispersing uniformly the copolymers (X) and (Y), which havebeen prepared separately, by an appropriate method. For example,extrusion melt blending, Banbury blending and the like can be applied.

[0065] The propylene-resin composition can also be obtained by so-calledmultiple stage polymerization in which polymerization conditions arechanged stepwise. For example, the resin composition can be obtained bypolymerizing component (A) first and subsequently polymerizing component(B) in the presence of the component (A) formed previously to obtain acopolymer (X), and then polymerizing a copolymer (Y) in the presence ofthe copolymer (X) formed previously.

[0066] The propylene-based resin composition of the present inventionmay optionally contain additives and resins other than the copolymers(X) and (Y). Examples of the additives include antioxidants, ultravioletabsorbers, antistatic agents, lubricants, nucleating agents, pressuresensitive adhesives, anti-clouding agents and antiblocking agents.Examples of the additional resins include olefin-based resins other thanthe copolymers (X) and (Y), e.g. ethylene-based resins.

[0067] The film of the present invention is a film having a layer madeof the above-mentioned propylene-based resin composition.

[0068] Examples of the film of the present invention include filmsconsisting of a single layer made of the propylene-based polymercomposition of the present invention and films comprising at least twolayers including a layer made of the composition of the presentinvention.

[0069] The method for producing the film of the present invention is notparticularly restricted and may be chosen depending upon the layerconstitution of the film. For example, available for the purpose areblow film formation, T-die film formation, calendering and the like,which have conventionally been employed for production of films.

[0070] Depending upon the layer constitution of a film to be produced,methods in which a film is formed only from the propylene-based resincomposition of the present invention by the above-mentioned techniquesand methods in which multiple layers (at least two layers) of thecomposition of the present invention and other resin material(s) areformed together into a film are applicable. The method for forming afilm comprising multiple layers is exemplified by conventionally usedcoextrusion, extrusion lamination, hot lamination and dry lamination.

[0071] In addition, a method in which a film or sheet which has beenprepared in advance is stretched to form a film is also available.Examples of methods for the stretching include unially or biaxiallystretching achieved by roll stretching, tenter stretching, tubularstretching or the like. In view of a balance of physical properties,e.g. low-temperature heat sealability, transparency and rigidity, of aresulting film, preferred are non-stretching coextrusion and biaxiallystretching.

[0072] An example of applications of the film of the present inventionis packaging. Examples of films for packaging include films forpackaging foodstuffs and films for packaging clothes. Preferred arefilms for packaging foodstuffs.

EXAMPLES

[0073] The present invention will be illustrated specifically below withreference to examples and comparative examples. However, the inventionis not restricted to these examples. The methods for preparing thesamples used in the examples and comparative examples and the methodsfor measuring physical properties are described below.

[0074] (1) Contents (Unit: % By Weight) of Components (A) and (B)

[0075] The contents of components (A) and (B) in a propylene-basedcopolymer (X) are determined from a material balance of polymerization.

[0076] (2) 1-Butene Content (Unit: % by Weight)

[0077] The content of 1-butene in a substance was determined from acharacteristic absorption of the substance at a wavenumber of 770 cm⁻¹by a method for measuring IR spectrum described in MacromoleculeHandbook (1995, published by Kinokuniya), page 619.

[0078] (3) Ethylene Content (Unit: % by Weight)

[0079] The content of ethylene in a substance was determined fromcharacteristic absorptions of the substance within the wavenumber rangeof from 720 to 732 cm⁻¹ by a conventional method with an infraredspectrophotometer using a standard sample.

[0080] (4) Melt Flow Rate (MFR, Unit: g/10 min)

[0081] MFR was measured according to JIS K7210 at a temperature of 230°C. and at an applied load of 21.18 N.

[0082] (5) Transparency (Haze, Unit: %)

[0083] Transparency was measured according to JIS K7105.

[0084] (6) Gloss (Unit: %)

[0085] Gloss was measured according to JIS K7105.

[0086] (7) Heat Seal Temperature (HST, Unit: ° C.)

[0087] A portion of a surface of a film and another of the same surfaceof the film were allowed to face in contact together and were heatsealed by pressing for 2 seconds under a load of 2 kg/cm²G using a heatsealer (manufactured by Toyo Seiki Seisaku-Sho, Ltd.) heated topredetermined temperatures (eleven points at 5° C. intervals between 65°C. and 115° C.). The resulting sample was conditioned overnight at 23°C. and at a humidity of 50%. Subsequently, the sample was measured for aseal temperature at which a peel resistance of 300 g/25 mm was detectedwhen peeling was carried out under the following conditions: atemperature of 23° C., a humidity of 50%, a peel speed of 200 mm/min anda peel angle of 180 degrees. The seal temperature obtained wasconsidered as a heat seal temperature.

[0088] (8) Blocking (Unit: kg/12 cm²)

[0089] A specimen obtained by bringing one surface of a film and theother surface of the film in contact together and processing at 60° C.for 3 hours under a load of 500 g/12 cm² was shear peeled. A maximumload (kg) was determined and indicated in kg/12 cm².

[0090] (9) Maximum Endothermic Peak Temperature (T, Unit: ° C.) andRatio of Amount of Main Heat Absorption to Amount of Total HeatAbsorption (Unit: %)

[0091] (9-1) Maximum Endothermic Peak Temperature (T, Unit: ° C.)

[0092] Measured was the temperature T (° C.) at which a maximumendothermic peak appears in a melting curve that was obtained bypreparing a 0.5 mm thick sheet by hot-press forming a material for test(namely, preheating the material at 230° C. for 5 minutes, increasingthe pressure up to 50 kgf/cm²G over 3 minutes and holing the pressurefor 2 minutes, and then cooling the composition at 30° C. for 5minutes), heat treating a 10 mg piece cut out from the resulting sheetat 220° C. for 5 minutes under a nitrogen atmosphere using adifferential scanning calorimeter (Model DSC-7, manufactured by PerkinElmer Co.), subsequently cooling to 150° C. at a temperature decreasespeed of 300° C./minute, holding at 150° C. for one minute, furthercooling to 50° C. at a temperature decrease speed of 5° C./minute,holding at 50° C. for one minute, and heating from 50° C. to 180° C. ata temperature increase speed of 5° C./minute.

[0093] (9-2) Ratio of Amount of Main Heat Absorption to Amount of TotalHeat Absorption (Unit: %)

[0094] In the resulting melting curve were determined the areasurrounded by the melting curve and a straight line (baseline) obtainedby joining a point at 53° C. and a point at 170° C., namely the amountof total heat absorption, and the area surrounded by the baseline andthe melting curve within the temperature range of from T−10 (° C.) toT+10 (° C.), centered at a temperature T (° C.) where a maximumendothermic peak appears, namely the amount of main heat absorption,from which the ratio was calculated according to the following formula.

Ratio of amount of main heat absorption to amount of total heatabsorption=(Amount of main heat absorption/Amount of total heatabsorption)×100

Example 1

[0095] [Synthesis of Solid Catalyst]

[0096] The atmosphere in a stainless reactor with a capacity of 200 Lequipped with a stirrer was replaced with nitrogen and then 80 L ofhexane, 6.55 mol of tetrabutoxytitanium, 2.8 mol of diisobutyl phthalateand 98.9 mol of tetrabutoxysilane were charged therein to form ahomogeneous solution. Then, 51 L of a solution of butylmagnesiumchloride of a concentration of 2.1 mol/L in diisobutyl ether was addeddropwise slowly over 5 hours while the temperature in the reactor waskept at 5° C. After completion of the dropping, stirring was continuedfor another 1 hour. Solid-liquid separation was conducted at roomtemperature and washing with 70 L of toluene was repeated three times.

[0097] Subsequently, toluene was removed so that the slurry contentbecame 0.6 kg/L. Thereafter, a mixed solution of 8.9 mol of di-n-butylether and 274 mol of titanium tetrachloride was added and then 20.8 molof phthalyl chloride was also added, followed by a three-hour reactionat 110° C. After the reaction, washing with toluene was repeated twiceat 95° C.

[0098] After adjustment of the slurry concentration to 0.6 kg/L, 3.13mol of diisobutyl phthalate, 8.9 mol of di-n-butyl ether and 137 mol oftitanium tetrachloride were added and a reaction was carried out at 105°C. for 1 hour. After the completion of the reaction, solid-liquidseparation was carried out at that temperature and washing with 90-Ltoluene was repeated twice at 95° C.

[0099] After adjustment of the slurry concentration to 0.6 kg/L, 8.9 molof di-n-butyl ether and 137 mol of titanium tetrachloride were added anda reaction was carried out at 95° C. for 1 hour. After the completion ofthe reaction, solid-liquid separation was carried out at thattemperature and washing with 90-L toluene was repeated three times atthe same temperature.

[0100] After adjustment of the slurry concentration to 0.6 kg/L, 8.9 molof di-n-butyl ether and 137 mol of titanium tetrachloride were added anda reaction was carried out at 95° C. for 1 hour.

[0101] After the completion of the reaction, solid-liquid separation wascarried out at that temperature and washing was repeated three times atthe same temperature using 90-L toluene, followed by additional washingwith 90-L of hexane three times. Subsequent drying under reducedpressure afforded 11.0 kg of solid catalyst component.

[0102] The solid catalyst component contained 1.89% by weight oftitanium atom, 20% by weight of magnesium atom, 8.6% by weight ofphthalic acid ester, 0.05% by weight of ethoxy group and 0.21% by weightof butoxy group, and had favorable particle properties free from finepowder.

[0103] [Preliminary Activation of Solid Catalyst]

[0104] To a SUS autoclave with a capacity of 3 L equipped with astirrer, 1.5 L of n-hexane which had been fully dewatered and degassed,37.5 mmol of triethylaluminum, 3.75 mmol oftert-butyl-n-propyldimethoxysilane and 15 g of the above-described solidcatalyst component were added. Subsequent to preliminary activation bycontinuously feeding 15 g of propylene over 30 minutes while keeping thetemperature in the reactor between 5° C. and 15° C., the resulting solidcatalyst slurry was transferred to a SUS autoclave with a capacity of200 L equipped with a stirrer, diluted by addition of 140 L of liquidbutane, and preserved at a temperature of 5° C. or lower.

[0105] [Polymerization of Propylene-Based Copolymer (X)]

[0106] (First Step)

[0107] In a SUS polymerization vessel with a capacity of 300 L equippedwith a stirrer, there were fed 35 kg/hr of liquid propylene, 13 kg/hr of1-butene and hydrogen in an amount such that the hydrogen concentrationof the gas phase portion was kept at 0.5 vol %. Further, 0.6 g/hr of thepreliminarily activated solid catalyst component was fed and slurrypolymerization using liquid propylene as a medium was continued at apolymerization temperature of 60° C. under conditions such that thesubstantial amount of slurry staying in the vessel was kept at 90 L. Theamount of the polymer formed during this operation was 2.0 kg/hr. Fromthe analysis of part of the polymer, the butene content was 7.7 mol %.The resulting slurry containing the polymer was transferred continuouslywithout being inactivated to a polymerization vessel for a second step.

[0108] (Second Step)

[0109] In a gas-phase fluidized bed reactor with a capacity of 1 m³equipped with a stirrer, 22.2 kg/hr of a propylene-based polymer (X-1)was obtained by feeding the solid catalyst component-containing polymertransferred from the reactor for the first step, 50 mmol/hr oftriethylaluminum and 5 mmol/hr of tert-butyl-n-propyldimethoxysilane andcontinuing the continuous polymerization under conditions such thatpropylene, hydrogen and 1-butene were fed so as to hold the amount ofpolymer contained in the fluidized bed to 80 kg, the polymerizationtemperature to 65° C., the polymerization pressure to 1.15 MPa, thehydrogen concentration in the gas phase to 2.5 vol % and the 1-butenecontent in the gas phase to 25 vol %. The 1-butene content in thepropylene-based polymer (X-1) was 20.0 mol %. The weight ratio of thepolymer obtained in the first step (component (A)) to the polymerobtained in the second step (component (B)) was determined from theamounts of the polymers in individual steps to be 10/90. The 1-butenecontent in component (B) was 21.8 mol %.

[0110] That is, in the propylene-based copolymer (X-1) obtained, thecontent of component (A) was 10% by weight, the content of component (B)was 90% by weight, the 1-butene content of component (A) was 7.7 mol %,the 1-butene content of component (B) was 21.8 mol %, and the 1-butenecontent in the propylene-based copolymer (X-1) was 20.0 mol %. Inmeasurement of a DSC curve of the copolymer (X-1), the ratio of theamount of main heat absorption to the amount of total heat absorptionwas 29%.

[0111] [Pelletization of Composition]

[0112] To 100 parts by weight of a powder obtained by mixing 90% byweight of the propylene-based copolymer (X-1) and 10% by weight ofSumitomo Noblen RW150XG (manufactured by Sumitomo Chemical Co., Ltd.,ethylene content 4.6% by weight) (Y-1), which is a propylene/ethylenerandom copolymer, 0.1 part by weight of calcium stearate, 0.05 part byweight of Irganox 1010 (manufactured by Ciba Specialty Chemicals), 0.1part by weight of 2,6-di-tert-butyl-4-methylphenol (BHT manufactured bySumitomo Chemical Co., Ltd.) and 0.4 part by weight of Tospearl 120(manufactured by GE Toshiba Silicones) were mixed and then melt kneaded,resulting in pellets. The pellets obtained had an MFR of 8.0 g/10 min.

[0113] [Preparation of Stretched Film]

[0114] The pellets obtained above and FS2011DG2 (polypropylene having amelting point of 159° C. and an MFR of 2.5 g/10 min) were used for asurface layer and a substrate layer, respectively. These weremelt-kneaded separately in different extruders at resin temperatures of230° C. for the surface layer and 260° C. for the substrate layer,respectively, and then were fed to one coextruding T-die. A resinextruded in two-kind two-layer constitution of surface layer/substratelayer from the T-die was cooled rapidly with a 30° C. cooling roll,thereby affording a cast sheet 1 mm thick.

[0115] The cast sheet obtained in the above manner was preliminarilyheated and then stretched 5 times in the longitudinal direction at astretching temperature of 125° C. using a difference in peripheral speedbetween rolls of the longitudinal stretching machine. Subsequently, thesheet was stretched 8 times in the transverse direction at a stretchingtemperature of 157° C. in an oven, followed by heat treatment at 165° C.Thereby obtained was a two-layer biaxially stretched film having asurface layer 1.5 μm thick and a substrate layer 20 μm thick, which wasthen wound up with a winder. The results of evaluation of physicalproperties of the resulting film are shown in Table 1.

Example 2

[0116] Pelletization, film formation and evaluation of physicalproperties were carried out in the same manner as Example 1 except usingblend proportions; propylene-based copolymer (X-1) of 65% by weight andpropylene/ethylene copolymer (Y-1) of 35% by weight. The pellets have anMFR of 8.0 g/10 min. The results are shown in Table 1.

Comparative Example 1

[0117] A propylene-1-butene copolymer (X-2) was obtained by asingle-stage gas phase polymerization using a titanium chloride typesolid catalyst system in the same manner as Example 1 described in JP,2-57770,B. The 1-butene content in the resulting copolymer was 19.2 mol%. In measurement of a DSC curve of the copolymer X-2, the ratio of theamount of main heat absorption to the amount of total heat absorptionwas 37%.

[0118] Pelletization, film formation and evaluation of physicalproperties were carried out in the same manner as Example 1 using thecopolymer (X-2) alone. The results are shown in Table 1. The pelletshave an MFR of 8.3 g/10 min. The heat seal temperature was high and theanti-blocking property was poor.

Comparative Example 2

[0119] Pelletization, film formation and evaluation of physicalproperties were carried out in the same manner as Example 1 except usingblend proportions, propylene-based copolymer (X-2) of 65% by weight andpropylene/ethylene copolymer (Y-1) of 35% by weight. The pellets have anMFR of 7.8 g/10 min. The results are shown in Table 1. The heat sealtemperature was high.

Comparative Example 3

[0120] Pelletization (MFR=8.2 g/10 min), film formation and evaluationof physical properties were carried out in the same manner as Example 1using the copolymer (X-1) alone. The pellets have an MFR of 8.2 g/10min. The results are shown in Table 1. The anti-blocking property waspoor. TABLE 1 Resin Composition MFR Haze Gloss HST Blocking X (wt %) Y(wt %) (g/10 min) (%) (%) (° C.) (kg/12 cm²) Example 1 X-1 (90) Y-1 (10)8.0 2.5 150 96 0.41 Example 2 X-1 (65) Y-1 (35) 8.0 2.7 150 95 0.31Comparative X-2 (100) — 8.3 2.5 150 99 0.72 Example 1 Comparative X-2(65) Y-1 (35) 7.8 2.8 151 101 0.43 Example 2 Comparative X-1 (100) — 8.22.3 151 96 0.58 Example 3

[0121] According to the present invention, a film can be obtained whichhas optical characteristics, e.g. transparency and gloss, equal to thoseof conventional polypropylene films and which is superior inlow-temperature heat sealability and antiblocking property.

What is claimed is:
 1. A propylene-based resin composition comprising:from 40 to 99% by weight of a propylene-based copolymer (X) consistingof from 1 to 30% by weight of component (A) that is a copolymericcomponent which is made up of propylene and an α-olefin having 4 or morecarbon atoms and which satisfies Requirement 1 defined below or acopolymeric component which is made up of propylene, an α-olefin having4 or more carbon atoms and ethylene and which satisfies Requirement 1and Requirement 2 defined below and from 70 to 99% by weight ofcomponent (B) that is a copolymeric component which is made up ofpropylene and an α-olefin having 4 or more carbon atoms and whichsatisfies Requirement 3 defined below or a copolymeric component whichis made up of propylene, an α-olefin having 4 or more carbon atoms andethylene and which satisfies Requirement 3 and Requirement 4 definedbelow, wherein the copolymer (X) satisfies Requirement 5 defined below,and from 1 to 60% by weight of a propylene-based copolymer (Y) made upof propylene and an α-olefin and/or ethylene, the copolymer (Y) having acontent of propylene of from 86 to 97% by weight and a combined contentof ethylene and the α-olefin of from 3 to 14% by weight, provided thateach of the percentages of the amounts of the component (A) and thecomponent (B) is based on the amount of the copolymer (X) and the sum ofthe percentages of the amounts of the components (A) and (B) is 100% byweight, each of the percentages of the amounts of the copolymer (X) andthe copolymer (Y) is based on the combined amount of the copolymers (X)and (Y), and the content of propylene in the copolymer (Y) and thecombined content of ethylene and the α-olefin in the copolymer (Y) arerespectively based on the combined amount of propylene, ethylene and theα-olefin in the copolymer (Y): Requirement 1: The content of α-olefinhaving 4 or more carbon atoms in the component is not less than 1 mol %but less than 15 mol %. Requirement 2: The content of ethylene in thecomponent is not more than 5 mol %. Requirement 3: The content ofα-olefin having 4 or more carbon atoms in the component is from 15 mol %to 30 mol %. Requirement 4: The content of ethylene in the component isnot more than 5 mol %. Requirement 5: In measurement of a DSC curve ofthe material, the amount of heat absorption within the temperature rangeof from T−10 (° C.) to T+10 (° C.) accounts for from 15 to 36% theamount of heat absorption within the temperature range of from 53° C. to170° C., wherein T denotes a temperature (° C.) at which a maximumendothermic peak appears.
 2. The propylene-based resin compositionaccording to claim 1, wherein the copolymer (X) is a copolymer such thatthe component (A) is polymerized in a first step and the component (B)is polymerized in a second step or in the second and later stepsperformed in the presence of the component (A) which has been formed inthe first step.
 3. The propylene-based resin composition according toclaim 2, wherein the copolymer (X) is a copolymer obtained by performingthe polymerization for forming the component (A) in the absence of aninert solvent and performing the polymerization for forming thecomponent (B) in a gas phase.
 4. The propylene-based resin compositionaccording to claim 1, wherein the copolymer (X) is a copolymer obtainedby polymerizing propylene and an α-olefin having 4 or more carbon atomsor polymerizing propylene, an α-olefin having 4 or more carbon atoms andethylene in the presence of a solid catalyst component containing Ti, Mgand halogen as essential components.
 5. A film having a layer made ofthe propylene-based resin composition according to claim 1.